Autoantibodies to FK506 binding protein 12 (FKBP12) in autoimmune diseases

Primary biliary cirrhosis: What do autoantibodies tell us?

Primary biliary cirrhosis (PBC) is a chronic, progressive, cholestatic, organ-specific autoimmune disease of unknown etiology. It predominantly affects middle-aged women, and is characterized by autoimmune-mediated destruction of small- and medium-size intrahepatic bile ducts, portal inflammation and progressive scarring, which without proper treatment can ultimately lead to fibrosis and hepatic failure. Serum autoantibodies are crucial tools for differential diagnosis of PBC. While it is currently accepted that antimitochondrial antibodies are the most important serological markers of PBC, during the last five decades more than sixty autoantibodies have been explored in these patients, some of which had previously been thought to be specific for other autoimmune diseases.

Comparative study of the cellular pharmacodynamics of calcineurin inhibitors between patients with chronic renal failure awaiting renal transplantation and cirrhosis patients awaiting liver transplantation

The in vitro response of peripheral blood mononuclear cells (PBMCs) to the suppressive effects of calcineurin inhibitors is known to correlate with the clinical efficacy of drugs used in renal transplantations. The present study was conducted to examine the differences of PBMC responses to calcineurin inhibitors between chronic renal failure (CRF) patients awaiting renal transplantation and cirrhosis patients awaiting liver transplantation. The study included 99 CRF patients awaiting renal transplantation and 27 cirrhosis patients awaiting liver transplantation. Twenty milliliters of venous blood was taken 1-7 days before transplantation. The in vitro drug concentrations giving 50% inhibition of PBMC blastogenesis stimulated with concanavalin A (IC(50)s) were calculated. The suppressive effects of tacrolimus against PBMC blastogenesis were more than 10-100 times stronger than those of cyclosporine. The median IC(50) value for cyclosporine against the CRF PBMCs was not significantly different from the median IC(50) value against the cirrhosis PBMCs. In contrast, tacrolimus sensitivity in cirrhosis PBMCs is approximately seven times higher than that in CRF PBMCs. The median IC(50) value for tacrolimus against cirrhosis PBMCs was significantly lower and therefore the effect was stronger in comparison to the CRF PBMCs (p < 0.001). These data suggest that the PBMCs of cirrhosis patients, in comparison to those of CRF patients, are highly sensitive to the suppressive effect of tacrolimus. However, PBMC sensitivity to cyclosporine was not significantly different between the CRF and cirrhosis patients. These observations raise the possibility that treatment with tacrolimus, rather than cyclosporine, may therefore be a better choice to reduce the risks of allograft rejection in liver transplantation.

Multimer formation by FKBP-12: roles for cysteine 23 and phenylalanine 36

FKBP-12 mediates the immunosuppressive actions of FK506 and rapamycin, and modulates the activities of the ryanodine, IP3 and type 1 TGF-ss receptors. Additionally, FKBP-12 possesses cis-trans peptidylprolyl isomerase (rotamase) activity. We have discovered that recombinant FKBP-12 readily forms a dimer and a small amount of trimer under nonreducing conditions. A mutant with substitution at the sole cysteine residue of FKBP-12 (C23S) did not form dimers or trimers. Using mutants with 5% or less rotamase activity, the formation of dimers was independent of enzymatic activity. The formation of trimers was abrogated by a F36Y substitution, even though dimer formation was preserved. Dimers were also observed with native FKBP-12 that was detached from rabbit skeletal muscle ryanodine receptors using FK590. The multimers of FKBP-12 could interact with molecular targets distinctly from the FKBP-12 monomer, for example, by facilitating the assembly of multimeric receptors or coordinating the activity of receptor subunits.

Pharmacological targeting of catalyzed protein folding: the example of peptide bond cis/trans isomerases

Peptide bond isomerases are involved in important physiological processes that can be targeted in order to treat neurodegenerative disease, cancer, diseases of the immune system, allergies, and many others. The folding helper enzyme class of Peptidyl-Prolyl-cis/trans Isomerases (PPIases) contains the three enzyme families of cyclophilins (Cyps), FK506 binding proteins (FKBPs), and parvulins (Pars). Although they are structurally unrelated, all PPIases catalyze the cis/trans isomerization of the peptide bond preceding the proline in a polypeptide chain. This process not only plays an important role in de novo protein folding, but also in isomerization of native proteins. The native state isomerization plays a role in physiological processes by influencing receptor ligand recognition or isomer-specific enzyme reaction or by regulating protein function by catalyzing the switch between native isomers differing in their activity, e.g., ion channel regulation. Therefore elucidating PPIase involvement in physiological processes and development of specific inhibitors will be a suitable attempt to design therapies for fatal and deadly diseases.

Autoantibody explosion in systemic lupus erythematosus: more than 100 different antibodies found in SLE patients

OBJECTIVE

Description of the various autoantibodies that can be detected in patients with systemic lupus erythematosus (SLE).

METHODS

A literature review, using the terms "autoantibody" and "systemic lupus erythematosus", was conducted to search for articles on autoantibodies in SLE, their target antigens, association with disease activity, or other clinical associations.

RESULTS

One hundred sixteen autoantibodies were described in SLE patients. These include autoantibodies that target nuclear antigens, cytoplasmic antigens, cell membrane antigens, phospholipid-associated antigens, blood cells, endothelial cells, and nervous system antigens, plasma proteins, matrix proteins, and miscellaneous antigens. The target of autoantibody, the autoantigen properties, autoantibody frequencies in SLE, as well as clinical associations, and correlation with disease activity are described for all 116 autoantibodies.

CONCLUSIONS

SLE is the autoimmune disease with the largest number of detectable autoantibodies. Their production could be antigen-driven, the result of polyclonal B cell activation, impaired apoptotic pathways, or the outcome of idiotypic network dysregulation.